Bistable cathode coupled switching gate generator



Feb. 9, 1960 F. E. SMITH 2,924,710

BISTABLE CATHODE COUPLED SWIZT'C HINGv GATE GENERATOR Filed Jan. 51,1957 12W hi4 I 4 5 5' i I l (b) H 'Y l l i i i s v l g l (c) INVENTOR.FREDERICK E. SMITH BISTABLE CATHODE COUPLED SWITCHING GATE GENERATORFrederick E. Smith, Southampton, Pa., assignor' to the United States of.America as represented by the Secretary of the Navy Application January'31, 1957, Serial No. 637,602

2 Claims. (Cl. 250-27) (Granted under Title 35, U.S. Code (1952), see.266) The invention described herein may be manufactured and used byorfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The present invention relates to a bi-stable cathodecoupled switchinggate generator lacking time constant networks for insuring an outputwhich is free of charge and discharge slopes.

One prior arrangement for performing the function of this inventionconsists of two separate cathode followers connected with their platesto a source of positive voltage and their cathodes connected throughindependent cathode resistors to a source of negative voltage. Each gridis connected to a source of switching voltage through individualcoupling condensers, and individual resistors are used as grid returnpaths to the source of positive voltage. The time constants of the gridnetworks are designed to allow an undistorted wave form to pass throughthem to the grid. The output wave for-ms at the cathodes are similar tothe input wave forms with the exception that the DC. levels have beenshifted allowing excursions both above and below ground potential. Thiscircuit in general meets the requirements of timing and voltageexcursions. However, any current drawn from the outputs will cause aresultant drop in voltage. The poor regulation makes it impossible toswitch more than one circuit, and when other sets of cathode followersare paralleled to give additional outputs, the unwanted signals are fedback from circuits being switched to the grid networks and appear in newoutputs. The output wave form does not have a flat top on the positiveexcursion due to grid current flow while the coupling condensersdischarge. This arrangement cannot respond over wide ranges of timeintervals without changing the values of the grid coupling networks. Andfinally, when the input switching voltage to these cathode followersfail, both of them come to rest in the on position. It is more desirableto have one stop on the off position and one on the on position fromconsiderations of circuit and application.

The cathode follower principleis followed in this invention in which twodual triodes are used to form a bi-stable switching generator. However,the arrangement is such that there is no need for and therefore there isa complete absence of time constant networks. This of course will insurean output which is free of charge and discharge slopes. In addition, theinventive circuit will follow a chain of pulses regardless of theirtiming interval. If a connection is made to one grid only of one of thetriodes, the circuit will respond to the first positive or negativepulse, depending upon which stable condition is present, and will notrespond to successive pulses of the same polarity until the stablecondition is changed by an intervening pulse of opposite polarity. Thisfeature is useful in count down applications. Other -advantages of theinventive circuit include that many of these circuits can be driven froma trigger source and no interaction will take place. The circuit canalso readily be stopped in either of its stable states by connecting oneor the other of the grids to the source of negative voltage and thecircuit will come to rest with the same output voltages as areexperienced while it is in operation. The circuit being switched can beconveniently monitored while in its static state. Finally, the circuitcan also be driven by any wave form capable of being differentiated.

It is thus a first object of the present invention to provide a novelbi-stable switching g ate generator capable of producing an output whichis free of charge and discharge slopes A further object of the presentinvention is, the provision of a cathode-coupled switching gategenerator which will follow a chain of pulses regardless of their timinginterval and regardless of their shape providing the wave form iscapable of differentiation.

Another object is to provide a bi-stable cathode-coupled switching gategenerator which is capable of a wide variety of applications and capableof producing a perfect square wave characteristic in the output.

A final object of the present invention is the provision of a bi-stable,cathode-coupled, switching gate generator for producing a perfect squarewave characteristic in the output and capable of following a chain ofpulses regardless of their timing interval, and Which will not respondto a succeeding pulse of the same polarity until the stable condition ischanged by an intervening pulse of opposite polarity.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawing in which:

Fig. 1 shows schematically a preferred embodiment of the instantinvention.

Fig. 2 shows graphically the wave forms at various points in thecircuit.

Referring to Fig. 1, there is shown the switching gate generatorconsisting of triodes V V V and V The plates of V and V; are connectedthrough resistors R and R respectively, to a source of positive voltageE The grids of triodes V and V are connected directly to the plates of Vand V respectively, while their plates are connected directly to E Thecathode of triode V is connected through resistor R to the grid of V Thecathode of triode V is connected through resistor R back to the grid oftriode V The control grids of triodes V and V; are connected throughresistors R and R re spectively, to a negative voltage source E Thecathodes of triodes V and V; are also connected through a commonresistor R to said negative voltage source E The input to the pulsegenerator is from terminal 10 through an input capacitor C to the gridof V Of course, it is understood the input through a similar arrangementmay be made into the grid of triode V The output of the generator may betaken at either the cathode of triode V or the cathode of triode V orboth, on output terminals 12 and 14, respectively.

Figure 2 shows the various waveforms at several points in the bi-stablegenerator of Fig. l. The input signal having the shape shown in Fig.2(a) is delivered at terminal 10. After differentiation by the action ofcapacitor C and resistors R and R the signal placed on the grid oftriode V resembles the signal shown in Fig. 2(b) as is understood in theart. The output waveforms Figs. 2(0) and 2(d) appear on terminals 12 and14, as described further below.

The generator shown in Fig. 1 operates as follows:

Upon the initial energization of the circuit, assume that conduction istaking place in the triode V Since the plate of this tube is connectedto the positive voltage E the cathode of V; will rise instantly inpotential and cure 3 rent will flow through resistors R and R Theconnection to the grid of V from the junction of the resistors R and Rcauses the voltage level on said grid to rise also, and conduction willthen also take place in triode V The voltage at the plate of V, willthereby drop due to the voltage drop in resistor R Through the plateconnection to the grid of triode V conduction is reduced through triodeV Due to this reduction, the cathode of triode V will drop in potentialbecause of current reduction throughresistors R and R This will resultin a voltage drop on the grid of triode V thereby causing a reduction ofcurrent flow through this tube. The plate voltage on triode V will thenrise and hence assist conduction through triode V as was assumed in thebeginning.

The foregoing described action occurs virtually instantaneously byvirtueof the lack of time constant net works to introduce condenser chargingand discharging factors. Therefore, the cathode potentials of triodes Vand V will resemble that shown in Figs. 2(a) and (d), respectively. Thevarious wave forms illustrated in Fig. 2 are arranged to show theirrelative synchronization.

The value of the common cathode resistor R in Fig. l is chosen to allowa positive bias to be present on the cathodes due to current flowthrough one or the other triodes V and V The division of resistance ofthe networks R R and R R has been selected to allow cutoff of onesection of the triode pair consisting of V and V when its associatedcathode follower V or V is at its negative extreme. It is evident thatas the process described above continues, the circuit becomes stablewith V and V conducting and V and V non-conducting. The samereasoningcould be applied to show V and V on and V and V off, thus revealing thebi-stable characteristics of the circuit.

When a positive trigger is applied to the grid of the off triode V thecircuit is changed to its alternate stable state. A negative triggerapplied to the on triode V; will serve the same purpose. It is obvious,therefore, that triggers can be applied to either or both grids oftriodes V 01' V and may be of either positive or negative polarity. Thecircuit will immediately fall into synchronism with the incomingtriggers and will follow any changes in timing interval.

It is seen that the generator described above is capable of following achain of pulses regardless of their timing interval, or, in other words,the generator is not limited to any particular range of frequencies. Inaddition, it is seen that the circuit provided is responsive only to thenext pulse which is different in polarity from the last pulse thatchanged the state of the generator. This feature is especially useful incount down applications.

There are several other distinct advantages of this circuit. The absenceof all time constant networks insures that there will always be anoutput which is free of slopes due to charge and discharge ofcondensers, and hence, always a perfectly formed square wave output.Since the triodes are cathode-follower types, the output will be of lowimpedance which is suitable for switching screen grids, plates andcontrol grids of subsequent stages. Other advantages of this circuit arereadily apparent. A plurality of these circuits can be driven from onetrigger source without any interaction taking place in view of theabsence of time constant networks. The generator can readily be stoppedin either of its stable states by connecting one or the other of thegrids of triodes V or V, to the source of negative voltage and thecircuit will then come to rest with the same output voltages which areexperienced while it is in operation. Circuits being switched can beconveniently monitored while in its static state. Finally, the circuitis capable of being driven by any wave form capable of beingdifferentiated.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and thatnumerous modifications or alterations may be made therein withoutdeparting from the spirit and scope of the invention as set forth in theappended claims. For example, the circuit may be adjusted for anydesired output voltage, impedance value, etc. for a particularapplication. In addition, the circuit can very easily be madefree-running rather than bi-stable by the addition of the appropriatetime constant network.

Hence, it is intended that all matter contained in the above descriptionas shown in the accompanying drawing shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

l. A bistable, switching gate generator comprising, in combination,first, second, third and fourth trigger means, each provided with atleast an anode, cathode, and control element, first and secondsubstantially resistive load means connected between said first andfourth trigger anodes, respectively, and a positive source of voltage,third substantially resistive means connecting said first and fourthtrigger cathodes to a negative source of voltage, means applying saidpositive source of voltage to said second and third trigger anodes,fourth substantially resistive means between said second trigger cathodeand said negative source of voltage, fifth substantially resistive meansbetween said third trigger cathode and said negative source of voltage,means connecting said first trigger anode to said second trigger controlelement, means connecting said fourth trigger anode to said thirdtrigger control element, and means connecting said first and fourthtrigger control elements to intermediate points in said fifth and fourthresistance means, respectively, thereby permitting successive positiveand negative pulses applied to said first trigger control element tocause conduction alternately in said first and third trigger means andsaid second and fourth trigger means, respectively.

2. A bistable, switching gate generator comprising, in combination,first, second, third and fourth trigger means, each provided with atleast an anode, cathode, and control element, first and secondsubstantially resistive load means connected between said first andfourth trigger anodes, respectively, and a positive source of voltage,third substantially resistive means connecting said first and fourthtrigger cathodes to a negative source of voltage, means applying saidpositive source of voltage to said second and third trigger anodes,fourth substantially resistive means between said second trigger cathodeand said negative source of voltage, fifth substantially resistive meansbetween said third trigger cathode and said negative source of voltage,means connecting said first trigger anode to said second trigger controlelement, means connecting said fourth trigger anode to said thirdtrigger control element, means connecting said first and fourth triggercontrol elements to intermediate points in said fifth and fourthresistance means, respectively, thereby permitting successive positiveand negative pulses applied to said first trigger control element tocause conduction alternately in said first and third trigger means andsaid second and fourth trigger means, respectively, and output means onsaid second trigger cathode.

References Cited in the file of this patent UNITED STATES PATENTS Re.23,770 Bergfors Ian. 12, 1954 2,540,539 Moore Feb. 6, 1951 2,545,924Johnstone Mar. 20, 1951 2,629,825 Eckert eta1 Feb. 24, 1953

